Wide area communications network for remote data generating stations

ABSTRACT

A wide area communications network communicating data from a plurality of network service modules through a plurality of remote cell nodes and intermediate data terminals to a central data terminal. The wide area communicates network collects network generated by a plurality of physical devices such as gas, water or electricity meters, located within a geographical area. The wide area communications network is a layered network have a hierarchical communications topology. The central data terminal controls network operation. Intelligence exists at all layers of the network, thereby easing the workload of the central data terminal. The intelligence attributed to each module is a function of the application of that module.

RELATED PATENTS

This application is a continuation of U.S. patent application08/454,678, filed May 31, 1995, having a title WIDE AREA COMMUNICATIONSNETWORK NETWORK FOR REMOTE DATA GENERATING STATIONS, now U.S. Pat. No.5,963,146 which is a continuation patent application of a patentapplication entitled, RADIO COMMUNICATION NETWORK FOR REMOTE DATAGENERATING STATIONS, having Ser. No. 08/271,545 and filing date Jul. 7,1994, now U.S. Pat. No. 5,553,094 which is a file wrapper continuationapplication of the patent application entitled RADIO COMMUNICATIONNETWORK FOR REMOTE DATA GENERATING STATIONS, having Ser. No. 08/124,495,filed Sep. 22, 1993, now abandoned and a cont. of patent applicationentitled, RADIO COMMUNICATION NETWORK FOR REMOTE DATA GENERATINGSTATIONS, having Ser. No. 07/732,183, filed Jul. 19, 1991, now abandonedwhich is a continuation-in-part application of a patent applicationentitled, RADIO COMMUNICATION NETWORK FOR REMOTE DATA GENERATINGSTATIONS, having Ser. No. 07/480,573, filed Feb. 15, 1990, now U.S. Pat.No. 5,056,107, which issued on Oct. 8, 1991. The benefit of the earlierfiling dates of the parent patent applications is claimed pursuant to 35U.S.C. § 120.

BACKGROUND OF THE INVENTION

This invention relates to a communications network for collecting datafrom remote data generating stations, and more particularly a radiobased system for sending data from a plurality of network servicemodules, with each network service module attached to a meter, andcommunicating through remote cell nodes and through intermediate dataterminals, to a central data terminal.

DESCRIPTION OF THE RELEVANT ART

Many attempts have been made in recent years to develop an automaticmeter reading system for utility meters such as used for electricity,gas and water, which avoids meter reading personnel inspecting andphysically note the meter readings. There are of course many reasons forattempting to develop a system of this type.

Most of the prior art systems have achieved little success. The systemwhich has achieved some success or is most widely used has an automaticmeter reading unit mounted on an existing meter at the usage site andincludes a relatively small transmitter and receiver unit of very shortrange. The unit is polled on a regular basis by a travelling readingunit which is carried around the various locations on a suitablevehicle. The travelling reading unit polls each automatic meter readingunit in turn to obtain stored data. This approach is of limited value inthat it requires transporting the equipment around the various locationsand hence only very infrequent, for example monthly, readings can bemade. The approach avoids a meter reader person actually entering thepremises to physically inspect the meter which is of itself of somevalue but only limited value.

Alternative proposals in which reading from a central location iscarried out have been made but have achieved little success. Oneproposal involves an arrangement in which communication is carried outusing the power transmission line of the electric utility. Communicationis, therefore, carried out along the line and polls each remote readingunit in return. This device has encountered significant technicaldifficulties.

Another alternative attempted to use the pre-existing telephone linesfor communication. The telephone line proposal has a significantdisadvantage since it must involve a number of other parties, inparticular the telephone company, for implementing the system. Theutility companies are reluctant to use a system which cannot be entirelycontrolled and managed by themselves.

A yet further system using radio communication has been developed byData Beam, which was a subsidiary of Connecticut Natural Gas. Thisarrangement was developed approximately in 1986 and has subsequentlyreceived little attention and it is believed that no installations arepresently operative. The system includes a meter reading device mountedon the meter with a transmitting antenna which is separate from themeter reading device. The transmitting antenna is located on thebuilding or other part of the installation site which enables theantenna to transmit over a relatively large distance. The system uses anumber of receiving units with each arranged to receive data from alarge number of transmitters, in the range 10,000 to 30,000. Thetransmitters, in order to achieve maximum range, are positioned to someextent directionally or at least on a suitable position of the buildingto transmit to the intended receiving station. This arrangement leads tousing a minimum number of receiving stations for optimum costefficiency.

The separate transmitter antenna, however, generated significantinstallation problems due to wiring the antenna through the building tothe transmitter and receiver. The anticipated high level of power usedfor transmitting involved very expensive battery systems or veryexpensive wiring. The proposal to reduce the excessive cost was to sharethe transmission unit with several utilities serving the building sothat the cost of the transmitter could be spread, for example, betweenthree utilities supplied to the building. Such installation requiresseparate utility companies to cooperate in the installation. While thismight be highly desirable, such cooperation is difficult to achieve on apractical basis.

In order to avoid timing problems, the meter reading units were arrangedto communicate on a random time basis. However, the very large number,up to 30,000 of meter reading units reporting to a single receivingstation, leads to a very high number of possible collisions between therandomly transmitted signals. The system, therefore, as proposed, withdaily or more often reporting signals could lose as many as 20% to 50%of the signals transmitted due to collisions or interference which leadsto a very low efficiency data communication. The use of transmitters atthe meter reading units which are of maximum power requires a largerinterference protection radius between systems using the same allocatedfrequency.

An alternative radio transmission network is known as ALOHA. ALOHA has anumber of broadcasting stations communicate with a single receivingstation, with the broadcasting stations transmitting at randomintervals. In the ALOHA system, collisions occur so that messages arelost. The solution to this problem is to monitor the retransmission ofthe information from the receiving station so that each broadcastingstation is aware when its transmission has been lost. Each broadcastingstation is then programmed to retransmit the lost information after apredetermined generally pseudorandom period of time. The ALOHA systemrequires retransmission of the information from the receiving station totake place substantially immediately and requires each broadcastingstation to also have a receiving capability.

Cellular telephone networks are implemented on a wide scale. Cellularsystems, however, use and allocate different frequencies to differentremote stations. While this is acceptable in a high margin use for voicecommunications, the costs and complications cannot be accepted in therelatively lower margin use for remote station monitoring. Thetechnology of cellular telephones leads to the perception in the artthat devices of this type must use different frequency networks.

While theoretically automatic meter reading is highly desirable, it is,of course, highly price sensitive and hence it is most important for anysystem to be adopted for the price per unit of particularly the largenumber of meter reading units to be kept to a minimum. The high cost ofhigh power transmission devices, receiving devices and battery systemsgenerally leads to a per unit cost which is unacceptably high.

OBJECTS OF THE INVENTION

A general object of the invention is a communications network forcommunicating data from a plurality of network service modules to acentral data terminal.

Another object of the invention is a communications network which issuitable for an automatic meter reading system.

A further object of the invention is a communications network forcollecting data from remote data generating stations that is simple andeconomic to install and maintain.

A still further object of the invention is a communications network forcollecting data from network service modules that is spectrum efficient,and has inherent communication redundancy to enhance reliability andreduce operating costs.

An additional object of the invention is an open architecturecommunication network which accommodates new technology, and allows thenetwork operator to serve an arbitrarily large contiguous ornon-contiguous geographic area.

SUMMARY OF THE INVENTION

According to the present invention, as embodied and broadly describedherein, a wide area communications network is provided for sending datafrom a plurality of network service modules to a central data terminal.The wide area communications network collects NSM data generated by aplurality of physical devices located within a geographical area. Thephysical devices may be, for example, a utility meter as used forelectricity, gas or water. The wide area communications networkcomprises a plurality of network service modules, a plurality of remotecell nodes, a plurality of intermediate data terminals, and a centraldata terminal. Each network service module is coupled to a respectivephysical device.

The network service module (NSM) includes NSM-receiver means,NSM-transmitter means, and NSM-processor means, NSM-memory means and anantenna. The NSM-receiver means, which is optional, receives a commandsignal at a first carrier frequency or a second carrier frequency. In apreferred mode of operation, the NSM-receiver means receives the commandsignal on the first carrier frequency for spectrum efficiency. The widearea communications network can operate using only a single carrierfrequency, i.e., the first carrier frequency. The command signal allowsthe oscillator of the NSM-transmitting means to lock onto the frequencyof the remote cell node, correcting for drift. Signalling data also maybe sent from the remote cell node to the network service module usingthe command signal.

The NSM-processor means arranges data from the physical device intopackets of data, transfers the data to the NSM-memory means, and usesthe received command signal for adjusting the first carrier frequency ofthe NSM transmitter. The NSM data may include meter readings, time ofuse and other information or status from a plurality of sensors. TheNSM-processor means, for all network service modules throughout ageographical area, can be programmed to read all the correspondingutility meters or other devices being serviced by the network servicemodules. The NSM-processor means also can be programmed to read peakconsumption at predetermined intervals, such as every 15 minutes,throughout a time period, such as a day. The NSM-memory means stores NSMdata from the physical device. The NSM-processor means can be programmedto track and store maximum and minimum sensor readings or levelsthroughout the time period, such as a day.

The NSM-transmitter means transmits at the first carrier frequency therespective NSM data from the physical device as an NSM-packet signal.The NSM-packet signal is transmitted at a time which is randomly orpseudorandomly selected within a predetermined time period, i.e., usinga one-way-random-access protocol, by the NSM-processor means. TheNSM-transmitter includes a synthesizer or equivalent circuitry forcontrolling its transmitter carrier frequency. The NSM-transmitter meansis connected to the antenna for transmitting multi-directionally theNSM-packet signals.

A plurality of remote cell nodes are located within the geographicalarea and are spaced approximately uniformly and such that each networkservice module is within a range of several remote cell nodes, and sothat each remote cell node can receive NSM-packet signals from aplurality of network service modules. The remote cell nodes preferablyare spaced such that each of the network service modules can be receivedby at least two remote cell nodes. Each remote cell node (RCN) includesRCN-transmitter means, RCN-receiver means, RCN-memory means,RCN-processor means, and an antenna. The RCN-transmitter means transmitsat the first carrier frequency or the second carrier frequency, thecommand signal with signalling data. Transmitting a command signal fromthe RCN-transmitter means is optional, and is used only if theNSM-receiver means is used at the network service module as previouslydiscussed.

The RCN-receiver means receives at the first carrier frequency amultiplicity of NSM-packet signals transmitted from a multiplicity ofnetwork service modules. Each of the NSM-packet signals typically arereceived at different points in time, since they were transmitted at atime which was randomly or pseudorandomly selected within thepredetermined time period. The multiplicity of network service modulestypically is a subset of the plurality of network service modules. TheRCN-receiver means also receives polling signals from the intermediatedata terminal, and listens or eavesdrops on neighboring remote cellnodes when they are polled by the intermediate data terminal.

The RCN-memory means stores the received multiplicity of NSM-packetsignals. The RCN-processor means collates the NSM-packet signalsreceived from the network service modules, identifies duplicates ofNSM-packet signals and deletes the duplicate NSM-packet signals. When apolling signal is sent from an intermediate data terminal (IDT), theRCN-transmitter means transmits at the first carrier frequency thestored multiplicity of NSM-packet signals as an RCN-packet signal.

When a first remote cell node is polled with a first polling signal bythe intermediate data terminal, neighboring remote cell nodes receivethe RCN-packet signal transmitted by the first remote cell node. Uponreceiving an acknowledgment signal from the intermediate data terminal,at the neighboring remote cell nodes, the respective RCN-processor meansdeletes from the respective RCN-memory means messages, i.e., NSM-packetsignals, received from the network service modules that have the samemessage identification number as messages transmitted in the RCN-packetsignal from the first remote cell node to the intermediate dataterminal.

The plurality of intermediate data terminals are located within thegeographic area and are spaced to form a grid overlaying the geographicarea. Each intermediate data terminal includes IDT-transmitter means,IDT-memory means, IDT-processor means and IDT-receiver means. TheIDT-transmitter means includes a synthesizer or equivalent circuitry forcontrolling the carrier frequency, and allowing the IDT-transmittermeans to change carrier frequency. The IDT-transmitter means transmitspreferably at the first carrier frequency, or the second carrierfrequency, the first polling signal using a first polling-accessprotocol to the plurality of remote cell nodes. When the first pollingsignal is received by a remote cell node, that remote cell node respondsby sending the RCN-packet signal to the intermediate data terminal whichsent the polling signal. If the intermediate data terminal successfullyreceives the RCN-packet-signal, then the IDT-transmitter means sends anacknowledgment signal to the remote cell node.

The IDT-receiver means receives the RCN-packet signal transmitted at thefirst carrier frequency from the remote cell node which was polled.Thus, after polling a plurality of remote cell nodes, the IDT-receivermeans has received a plurality of RCN-packet signals.

The IDT-memory means stores the received RCN-packet signals. TheIDT-processor means collates the NSM-packet signals embedded in theRCN-packet signals received from the plurality of remote cell nodes,identifies duplicates of NSM-packet signals and deletes the duplicateNSM-packet signals, i.e., messages from network service modules thathave the same message identification number. In response to a secondpolling signal from a central data terminal, the IDT-transmitter meanstransmits a plurality of RCN-packet signals as an IDT-packet signal tothe central data terminal.

The central data terminal (CDT) includes CDT-transmitter means,CDT-receiver means, CDT-processor means and CDT-memory means. TheCDT-transmitter means transmits sequentially the second polling signalusing a second polling access protocol to each of the intermediate dataterminals. The CDT-receiver means receives a plurality of IDT-packetsignals. The central data terminal, intermediate data terminals and theremote cell nodes may be coupled through radio channels, telephonechannels, fiber optic channels, cable channels, or other communicationsmedium. The CDT-processor means decades the plurality of IDT-packetsignals as a plurality of NSM data. The CDT-processor means alsoidentifies duplicates of NSM data and deletes the duplicate NSM data.The CDT-memory means stores the NSM data in a data base.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention also may be realized andattained by means of the instrumentalities and combinations particularlypointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate preferred embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

FIG. 1 illustrates the hierarchial communications network topology;

FIG. 2 is a network service module block diagram;

FIG. 3 is a representative NSM-data packet;

FIG. 4 is a listing or representative applications supported by thecommunications network;

FIG. 5 is a schematic diagram of a network service module;

FIG. 6 shows a front elevation view of an electricity utility meter witha detection unit;

FIG. 7 shows a bottom plan view of the electricity utility meter;

FIG. 8 is an illustration of a typical printout of information obtainedby the network service module of FIG. 1;

FIG. 9 is a remote cell node block diagram;

FIG. 10 is an intermediate data terminal block diagram;

FIG. 11 is a central data terminal block diagram;

FIG. 12 shows the configuration of the communications network forserving widely separated geographic areas; and

FIG. 13 illustrates a typical communications network with gradual growthin the number of areas served.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals indicate likeelements throughout the several views.

A wide area communications network communicates data from a plurality ofnetwork service modules to a central data terminal. The wide areacommunications network collects NSM data generated by a plurality ofphysical devices located within a geographical area. The wide areacommunications network, as illustratively shown in FIG. 1, is a layerednetwork having a hierarchial communications topology comprising aplurality of network service modules 110, a plurality of remote cellnodes 112, a plurality of intermediate data terminals 114, and a centraldata terminal 120. The physical devices may be, for example, a utilitymeter as used for electricity, gas or water.

The central data terminal controls network operation. Intelligenceexists at all layers of the network, thereby easing the workload of thecentral data terminal. The intelligence attributed to each module is afunction of the application of that module.

Network Service Module

Information is acquired at the lowest level of the wide areacommunications network of FIG. 1, and the network service module 110performs the data acquisition functions. Network service modules 110include meter service modules for electricity, gas and water, a servicedisconnect module, a load management module, an alarm monitoring module,or any other module that can be used with the wide area communicationsnetwork.

The network service modules 110 are linked to the wide areacommunications network via high frequency radio channels, typically inthe 928 MHz-952 MHz band, as well as related frequencies in the 902MHz-912 MHz and 918 MHz-928 MHz bands. Radio channels in these bands arethe preferred communications medium because use of radio communicationseliminates the need for physical connections to the service moduleswhich drastically reduces installation costs compared to othercommunication media such as telephone, cable networks and power linecarriers. Also, operation in the high frequency bands permits the use ofsmall antennas so that retrofitting standard watt hour meters issimplified. Radio communication channels in other bands may work equallyas well, however.

In the exemplary arrangement shown in FIG. 2, the network service module(NSM) 110 includes NSM-receiver means, NSM-transmitter means,NSM-processor means, NSM-memory means and an NSM antenna 322. TheNSM-transmitter means and the NSM-receiver means are coupled to the NSMantenna 322. The NSM-processor means is coupled to the NSM-transmittermeans, NSM-receiver means, NSM-memory means and the physical device. Thephysical device is shown as basic 320 and other sensors 322, andapplication control interface 324. The network service module alsoincludes an AC power supply 310 and a back-up battery power supply 312.

The NSM-receiver means is embodied as an NSM receiver 316, and isoptional. If an NSM receiver 316 is included with the network servicemodule, then the NSM receiver 316 can be used for receiving a commandsignal, which includes signalling data. The command signal can betransmitted at either a first carrier frequency or a second carrierfrequency. Normally the first carrier frequency is used by theNSM-transmitter means for transmitting to a remote cell node. In apreferred embodiment, the NSM receiver 316 receives the command signalon the first carrier frequency for spectrum efficiency. Thus, the widearea communications network can operate using only a single carrierfrequency, i.e., the first carrier frequency. The command signal canprovide a time reference for updating a local clock, and serve as afrequency reference to the network service module. Signalling data, suchas manage service disconnect or control loads, also may be sent from theremote cell node to the network service module using the command signal.While the network service modules could be polled by the command signal,in general, such polling is not required and preferably not used withthe present invention.

The NSM-processor means, which is embodied as an NSM controller 314,arranges data from the physical device into packets of data, andtransfers the data to the NSM-memory means which is embodied as an NSMmemory 315. The NSM controller 314 may be a microprocessor or equivalentcircuit for performing the required functions. The NSM controller 314uses the received command signal for adjusting and setting the firstcarrier frequency of the NSM transmitter. The NSM data may include meterreadings, time of use and other information or status from a pluralityof sensors. The NSM controllers 314, for each network service modulethroughout a geographical area, can be programmed to read all thecorresponding utility meters or other devices being serviced by thenetwork service module, respectively. The NSM controller 314 can beprogrammed to read peak consumption at predetermined intervals, such asevery 15 minutes, throughout a time period, such as a day. The NSMcontroller 314 also can be programmed to track and store maximum andminimum sensor readings or levels throughout the time period, such as aday.

The NSM memory 315 stores NSM data from the physical device. NSM datamay include meter reading data and time of use (TOU) and otherinformation or status from a plurality of sensors. The NSM memory 315may be random access memory (RAM) or any type of magnetic media or othermemory storage devices known in the art. The NSM controller 314 uses thereceived command signal for adjusting the first carrier frequency of theNSM transmitter 318.

The NSM-transmitter means is embodied as an NSM transmitter 318. The NSMtransmitter 318 transmits at a first carrier frequency the respectiveNSM data from the physical device in brief message packets called anNSM-packet signal. The NSM-packet signal might have a time duration of100 milliseconds, although any time duration can be used to meetparticular system requirements. The NSM-packet signal transmitted by theNSM transmitter 318 follows a generic or fixed format, and arepresentative message packet is illustrated in FIG. 3. Included in themessage is: preamble; opening frame; message type; messageidentification; service module type; message number; service moduleaddress; data field; error detection; and closing frame.

The NSM transmitter 318 is connected to an NSM antenna 322 fortransmitting multi-directionally the NSM-packet signals. The NSMtransmitter 318 includes a synthesizer or equivalent circuitry forcontrolling its transmitter carrier frequency and schedule.

The NSM-packet signal is transmitted at a time which is randomly orpseudorandomly selected within a predetermined time period, i.e., usinga one-way-random-access protocol, by the NSM-processor means. In orderto simplify network operation and reduce costs, the wide areacommunications network does not poll individual network service modules.Rather, each network service module report s autonomously at a rateappropriate for the application being supported. Routine reports aretherefore transmitted randomly or pseudorandomly at fixed averageintervals, while alarm signals are transmitted immediately followingdetection of alarm conditions. Alarm signals may be transmitted severaltimes with random delays. This avoids interference among alarm messagesif many alarms occur simultaneously, as in an area-wide power outage.

As an alternative arrangement, the network service module may beprogrammed to transmit three different types of messages at differentintervals. The first type of message can relate to the accumulated usageinformation. The second type of message can relate to an alarm conditionwhich is basically transmitted immediately. The alarm conditions thatoccur might relate to a tamper action or to the absence of electricalvoltage indicative of a power failure. The third type of informationwhich may be transmitted less frequently can relate to the housekeepinginformation.

After preparing the packet of data for transmission, the controller 314is arranged to hold the data packet for a random period of time. Thisrandom period can be calculated using various randomizing techniquesincluding, for example, a psuedo-random sequence followed, for example,by an actual random calculation based upon the rotation of the meteringdisk at any particular instant. In this way each of the network servicemodules is arranged to transmit at a random time. The controller 314 isarranged so that the transmission does not occur within a particularpredetermined quiet time so that none of the network service modules isallowed to transmit during this quiet time. This quiet time could be setas one hour in every eight hour period. In this way after an eight hourperiod has elapsed, each of the network service modules would transmitat a random time during the subsequent seven hours followed by a quietone hour.

Network capacity or throughput is limited by the probability of messagecollisions at each remote cell node 112. Because all network servicemodules 110 share a single carrier channel and transmit at random times,it is possible for several network service modules 110 within a range ofa particular remote cell node 112 to transmit simultaneously and tocollide at the remote cell node. If the received signal levels arecomparable, the overlapping messages will mutually interfere, causingreceive errors and both messages will be lost. However, if one signal issubstantially stronger than the other, the stronger signal will besuccessfully received. Moreover, since both signals are received by atleast two and preferably four of the remote cell nodes, the probabilityof both messages being received is fairly high unless the networkservice modules are in close spatial proximity. During an interval T,each transmitter within a cell surrounding a single remote cell nodesends a single randomly timed message of duration M to several potentialreceive stations.

N=no. of transmitters/cell

M=message duration (seconds)

T=message interval

P_(c)=probability of collision

P_(s)=probability of no collision

Once any Transmitter, T_(i), starts transmitting the probability thatanother particular transmitter, T_(j), will complete or start anothertransmission is $\frac{2M}{T}.$

The probability that there will be no collision is$1 - {\frac{2M}{T}.}$

If there are N−1 other transmitters the probability of no collision,P_(s), is given by$P_{s} = \left( {1 - \frac{\left( \left. {2M} \right) \right)^{N - 1}}{T}} \right)$

For large N$P_{s} - \left( {1 - \frac{\left( \left. {2M} \right) \right)^{N}}{T}} \right.$

For a given Transmitter, T_(i), the probability of a collision occurringduring the interval T is$P_{c} = {{1 - P_{s}} = {1 - \left( {1 - \frac{\left( \left. {2M} \right) \right)^{N}}{T}} \right.}}$

The probability of collisions occurring on An successive tries is

P_(cn)=(P_(c))^(An)

For M=0.3 Sec T=8 hrs.=28.8×10³ secs.$P_{s} = \left( {{1 - {\frac{\left( \left. {2M} \right) \right)^{N}}{T}\quad 1} - {2.08 \times 10^{- 5}}} = ({.999979})^{N}} \right.$

N Ps Pcl Pc2 Pc3 100 .9979 .0021   4 × 10⁻⁶   8 × 10⁻⁹ 200 .9958 .00421.6 × 10⁻⁵ 6.4 × 10⁻⁸ 500 .9896 .0104 10⁻⁴ 10⁻⁶ 1,000 .9794 .0206   4 ×10⁻⁴   8 × 10⁻⁶ 2,000 .9591 .041 1.6 × 10⁻³ 6.8 × 10⁻⁵ 5,000 .9010 .0999.8 × 10⁻³ 9.7 × 10⁻⁴ 10,000 .811 .189 3.5 × 10⁻² 6.7 × 10⁻³

From the viewpoint of a remote cell node, the number of transmitters,N_(T), whose signal level exceeds the receiver noise level and can,therefore, be received reliably depends on:

(a) the density of transmitters;

(b) transmit power level;

(c) propagation path loss;

(d) background noise.

Propagation path loss is highly variable due to attenuation, reflection,refraction and scattering phenomena which are a function of terrain,building structures, and antenna location. Some of these parameters caneven vary on a diurnal and seasonal basis.

In estimating network performance however, the simple message collisionmodel is not completely accurate because:

1. random noise bursts from various sources can obscure messages whichdo not collide;

2. some colliding message signals will be of sufficiently differentamplitude that the stronger signal will still be received correctly.

A statistical model can be developed to provide data by whichdetermination can be made of the best location and number of remote cellnodes for a particular geographical location. Thus, the model caninclude data relating to house density the N− value defined aboverelating to the attenuation of the signal, the location and presence oftrees.

FIG. 4 is an illustrative listing of applications supported by thenetwork service module within the wide area communications network. Thefollowing is a detailed discussion of the electricity meter application.

Network Service Module with an Electricity Meter

A network service module 110 schematically is shown in FIG. 5 and ismounted in a suitable housing 211 illustrated in FIGS. 6 and 7 with thehousing including suitable mounting arrangement for attachment of thehousing into the interior of a conventional electricity meter 212. Eachnetwork service module is coupled to a respective physical device. InFIG. 6, the physical device is an electricity meter 212.

Referring to FIGS. 5, 6 and 7 the electricity meter 212 includes anouter casing 213 which is generally transparent. Within the casing isprovided the meter system which includes a disk 214 which rotates abouta vertical axis and is driven at a rate dependent upon the current drawnto the facility. The numbers of turns of the disk 214 are counted by acounting system including mechanical dials 215. The meter is ofconventional construction and various different designs are well knownin the art.

An antenna 217 is mounted on a bracket 216 carried on the housing insidethe cover 213. The antenna 217 as shown is arc-shaped extending aroundthe periphery of the front face. Other antenna configurations arepossible.

As illustrated in FIG. 6, the antenna 217 is mounted within the cover213 of the meter. Thus the NSM antenna 217 is mounted on the supportstructure itself of the network service module 110. This enables thenetwork service module 110 to be manufactured relatively cheaply as anintegral device which can be installed simply in one action. However,this provides an NSM antenna 217 which can transmit only relativelyshort distances. In addition, the power level is maintained inrelatively low value of the order of 10-100 milliwatts, the energy forwhich can be provided by a smaller battery system which is relativelyinexpensive. An NSM antenna 217 of this type transmitting at the abovepower level would have a range of the order of one to two kilometers.

The network service module 110 is in a sealed housing which preventstampering with the sensors, microprocessor 220 and memory 221 locatedwithin the housing 211.

Turning now to FIG. 5, the network service module optionally may includea detection device which uses the microprocessor 220 which hasassociated therewith a storage memory 221. An essential sensor is formeter reading, for measuring the amount of electricity, amount of wateror amount of gas consumed. Such a sensor alleviates having a meterreader person, by allowing the system to automatically report the amountof usage of the physical device.

Any number of sensors may be provided for detection of tampering eventswith the network service module of the present invention, and thesensors may be adapted for electricity, gas, water or otherapplications. For the most part, information reported by the varioussensors would be considered low data rate. The wide area communicationsnetwork supports distributed automation functions including basic meterreading, time of use meter reading, service connect and disconnectoperations, alarm reporting, theft of service reporting, load research,residential load control commercial and industrial load curtailment, anddistributed supervisory control and data acquisition (SCADA).Furthermore, the wide area communications network is readily expandableto support new applications as they are developed.

While the emphasis, by way of example, is automatic meter reading and onmeasuring time of use of an electricity meter, other functions such as15-minute peak consumption recording, line power monitoring, i.e.,outage and restoration, tamper sensing and timekeeping are supported.

The following is a representative listing of possible sensors that maybe used with the network service module of the present invention. Eachsensor is optional, and to a person skilled in the art, variants may beadded to the network service module of the present invention. Forexample, FIG. 6 illustratively shows a temperature sensor 227 and abattery sensor 228; however, each sensor 227, 228 may be substituted byor may be in addition to other possible sensors from the followingrepresentative listing of sensors.

(a) A tilt sensor 222 detects movement of the housing through an anglegreater than a predetermined angle so that once the device is installedindication can be made if the device is removed or if the meter isremoved from its normal orientation.

(b) A field sensor 223 detects the presence of an electric field. Unlessthere is power failure, the electric field sensor should continue todetect the presence of an electric field unless the meter is removedfrom the system.

(c) An acoustic sensor 224 detects sound. The sounds detected aretransmitted through a filter 225 which is arranged to filter by analogor digital techniques the sound signal so as to allow to pass throughonly those sounds which have been determined by previous experimentationto relate to cutting or drilling action particularly on the cover.

(d) A magnetic sensor 226 detects the presence of a magnetic field. Amagnetic field is generated by the coils driving the disk 214 so thatmagnetic fields should always be present unless the meter has beenby-passed or removed. As is well known, the rate of rotation of the diskis dependent upon the magnetic field and, therefore, this rate ofrotation can be varied by changing the magnetic field by applying apermanent or electromagnet in the area of the meter to vary the magneticfield. The sensor 226 is, therefore, responsive to variations in themagnetic field greater than a predetermined amount so as to indicatethat an attempt has been made to vary the magnetic field adjacent thedisk to slow down the rotation of the disk.

(e) A heat sensor 227 detects temperature so that the temperatureassociated with a particular time period can be recorded. A batterylevel sensor is indicated at 228. The sensors 226, 227 and 228communicate information through analog digital converter 328 to themicroprocessor 220. The information from sensors 227 and 228 can becommunicated to provide “housekeeping” status of the operation of theunit. The temperature sensor 227 can be omitted if required and thisinformation replaced by information gained from a public weatherinformation source. In some cases the meter is located inside thebuilding and hence the temperature will remain substantially constantwhereas the outside temperature is well known to vary consumption quitedramatically.

(f) A consumption sensor comprises a direct consumption monitor 229which can be of a very simple construction since it is not intended toact as an accurate measure of the consumption of the electricity used.The direct consumption monitor 229 can, therefore, simply be a devicewhich detects the value of the magnetic field generated on theassumption this is proportional to the current drawn. The directconsumption value obtained can then be competed with a measurement ofthe consumption as recorded by the rotation of the disk 214. In theevent that the direct consumption monitor 229 provides a sum of theconsumption over a time period which is different from the consumptionmeasured by rotation of the disk 214 by an amount greater than apredetermined proportion then the direct consumption monitor can be usedto provide a tamper signal. This would be indicative for example of amechanical tag applied to the disk to reduce recorded consumption.

(g) A reverse sensor 230, discussed in more detail hereinafter, detectsreverse rotation of the disk 214 and provides an input to themicroprocessor on detection of such an event.

(h) A cover sensor 231 is used to detect the continual presence of thecover 213. The cover sensor comprises a light emitting diode (LED) 232which generates a light beam which is then reflected to a photo diode233. The absence of the reflected beam at the photo diode 233 isdetected and transmitted as a tamper signal to the microprocessor. Thereflected beam is generated by a reflective strip 234 applied on theinside surface of the cover adjacent the diode 232 as shown in FIG. 6.

The above sensors thus act to detect various tampering events so thatthe presence of such tampering events can be recorded in the storagememory 221 under the control of the microprocessor 220.

The microprocessor 220 also includes a clock signal generator 335 sothat the microprocessor 220 can create a plurality of time periodsarranged sequentially and each of a predetermined length. In the exampleof the present invention shown the time periods are eight hours inlength and the microprocessor 220 is arranged to record in each eighthour period the presence of a tamper event from one or more of thetamper signals.

As shown in FIG. 8 the series of the predetermined time periods isrecorded with the series allocated against specific dates and each eighthour period within the day concerned having a separate recordinglocation within the storage memory 221. One such series is shown in FIG.8 where a number of tampering events 236 are indicated. The print-outthus indicates when any tampering event 236 has occurred and in additionthen identifies which type of tampering event has taken place.

The rotation of the disk 214 also is detected to accurately record thenumber of rotations of the disk both in a forward and in a reversedirection. In FIG. 8, a table 237 shows in graphical form the amount ofrotation of a disk recorded in eight hour periods as previouslydescribed. For one period of time the disk is shown to rotate in areverse direction 238. Whenever the disk rotates in a reverse direction,the reverse rotation subtracts from the number of turns counted on theconventional recording system 215 shown in FIG. 6.

As shown in FIGS. 6 and 7, detection of the rotation of the disk iscarried out by the provision of a dark segment 239 formed on theundersurface of the disk leaving the remainder of the disk as areflective or white material. The detection system thus provides a pairof light emitting diodes 240, 241 which are positioned on the housing soas to direct light onto the underside of the disk. The light emittingdiodes 240, 241 are angularly spaced around the disk. The diodes areassociated with the photo diodes 242, 243 which receive light when thedisk is positioned so that the light from the associated light emittingdiode 240, 241 falls upon the reflective part of the disk and that lightis cut off when the dark part of the disk 214 reaches the requisitelocation. Basically, therefore, one of the pairs of light emittingdiodes 240, 241 and photo diodes 242, 243 is used to detect the passageof the dark segment that is, of course, one rotation of the disk. Thedirection of rotation is then detected by checking with the other of thepairs as the dark segment reaches the first of the pairs as to whetherthe second pair is also seeing the dark segment or whether it is seeingthe reflective part. Provided the sensors are properly spaced inrelation to the dimension of the segment, therefore, this indicates thedirection which the disk rotated to reach the position which is detectedby the first pair of diodes.

In order to conserve energy, the sensors are primarily in a samplingmode using an adaptive sensing rate algorithm. In one example the darkor non-reflective segment is 108° of arc and there is provided a 50°displacement between the sensors. In a practical example of aconventional meter, the maximum rotation rate is of the order of 2 rps.A basic sample interval can be selected at 125 m/sec, short enough toensure at least one dark sample is obtained from the dark segment. Inoperation, only the first pair of sensors is sampled continuously. Whena dark response is observed, a second confirming sample is obtained andthe sample rate increased to 16 pps. As soon as a light segment of thedisk is sensed, the second sensor is sampled. The second sensor stillsees the dark segment then cw rotation is confirmed while if a lightsegment is observed then ccw rotation is indicated.

At slower speeds, the algorithm results in a sample rate of 8 pps for70% of a rotation and 16 pps for 30% of a rotation for the first pair ofsensors plus two samples for direction sensing for the second pair. Foran annual average consumption of 12,000 kwh, the disk rotatesapproximately 1.6 million times.

In order to sense the presence of stray light which could interfere withmeasurements, the photo diode output is sampled immediately before andimmediately after the LED is activated. If light is sensed with the LEDoff, stray light is indicated an alarm may be initiated after confirmingtest. The latter may include a test of other sensors such as the opticalcommunication port sensor discussed hereinafter.

As shown in FIG. 5 communication from the meter reading unit is carriedout by radio transmission from the microprocessor 220 through amodulation device 250 which connects to the antenna 322. Thetransmission of the signal is carried under control of themicroprocessor 220. Modulation carried out by the modulation device 250can be of a suitable type including, for example, phase modulation usingphase shift keying (PSK) such as binary PSK (BPSK), frequency modulationusing frequency shift keying (FSK), such as, for example, binary FSK, orspread spectrum modulation in which the signals are modulated onto anumber of separate frequencies at timed intervals so that no singlefrequency channel is used. This allows the system to be used without theallocation of a dedicated frequency so that the signal appears merely asnoise to receivers which do not have access to the decoding g algorithmby which the signal can be recovered from the different frequencies onwhich it is transmitted.

Remote Cell Node

A plurality of remote cell nodes 112 are located within the geographicalarea and are spaced approximately uniformly and such that each networkservice module 110 is within a range of several remote cell nodes 112 toprovide overlapping coverage. The remote cell nodes 112 typically mightbe spaced at 0.5 mile intervals on utility poles or light standards.Each remote cell node 112 provides coverage over a limited area muchlike the cell in a cellular telephone network. Remote cell nodes 112preferably are spaced to provide overlapping coverage, so that on anaverage, each NSM-packet signal transmitted by a network service module110 is received by three or four remote cell nodes 112, even in thepresence of temporary fading. As a consequence, erection of a tallbuilding near a network service module 110 has little or no effect onmessage reception, nor does the failure of a remote cell node 112 resultin loss of NSM-packet signals or NSM data.

As illustratively shown in FIG. 9, each remote cell node (RCN) 112 ofFIG. 1 includes RCN-transmitter means, RCN-transmitter means,RCN-receiver means, RCN-memory means, RCN-processor means and an RCNantenna 422. The RCN-transmitter means, RCN-receiver means, RCN-memorymeans and RCN-processor means may be embodied as an RCN transmitter 418,RCN receiver 416, RCN memory 415 and RCN processor 414, respectively.The RCN transmitter 418 and the RCN receiver 416 are coupled to the RCNantenna 422. The RCN processor 414 is coupled to the RCN transmitter418, RCN receiver 416, and RCN memory 415.

The RCN transmitter 418, under the control of the RCN processor 414,transmits at the first carrier frequency or the second carrier frequencya command signal. The choice of frequency depends on which frequency isbeing used for the NSM receiver 316 at each of the plurality of networkservice modules 110. Transmitting a command signal from the RCNtransmitter is optional, and is used if the NSM receiver 316 is used atthe network service module 110. The command signal can includesignalling data being sent to network service modules 110. Thesignalling data may require the network service module 110 to transmitstatus or other data; set reporting time period, e.g. from an eight hourperiod to a four hour period; and any other command, control or“housekeeping” jobs as required.

The RCN receiver 416 receives at the first carrier frequency amultiplicity of NSM-packet signals transmitted from a multiplicity ofnetwork service modules 110. Each of the multiplicity of NSM-packetsignals typically are received at different points in time, since theyare transmitted at a time which is randomly or pseudorandomly selectedwithin the predetermined time period. The multiplicity of networkservice modules 110 usually is a subset of the plurality of networkservice modules 110. Received NSM-packet signals are time stamped by theRCN processor 414 and temporarily stored in the RCN memory 415 beforebeing transmitted to the next higher network level. The RCN receiver 416also receives polling signals from the intermediate data terminal, andlistens or eavesdrops on neighboring remote cell nodes when they arepolled by the intermediate data terminal.

The RCN processor 414 collates the NSM-packet signals received from thenetwork service modules, identifies duplicates of NSM-packet signals anddeletes the duplicate NSM-packet signals. The RCN processor 414 controlsthe RCN transmitter 418 and RCN receiver 416. The RCN memory 415 storesthe received multiplicity of NSM-packet signals. Thus each remote cellnode 112 receives, decodes and stores in RCN memory 415 each of theseNSM-packet signals as received from the network service modules 110.

The remote cell node comprises simply a suitable resistant casing whichcan be mounted upon a building, lamp standard or utility pole at asuitable location in the district concerned. The remote cell node can bebattery powered with a simple omni-directional antenna as an integralpart of the housing or supported thereon.

Information accumulated at remote cell nodes 112 periodically isforwarded via a polled radio communications link to a higher levelnetwork node, as illustrated in FIG. 1, termed an intermediate dataterminal 114. The intermediate data terminals 114 are spaced typicallyat 4 mile intervals and can be conveniently sited at substations,providing coverage for up to 100 cells. Remote cell nodes also receivetiming information and command signals from intermediate data terminals.

When a polling signal is sent from an intermediate data terminal 114,the RCN transmitter 418 transmits at the first carrier frequency thestored multiplicity of NSM-packet signals as an RCN-packet signal to theintermediate data terminal 114.

When a first remote cell node is polled with a first polling signal bythe intermediate data terminal, neighboring remote cell nodes 112receive the RCN-packet signal transmitted by the first remote cell node.Upon receiving an acknowledgment signal from the intermediate dataterminal that polled the first remote cell node, at the neighboringremote cell nodes 112 the respective RCN processor deletes from therespective RCN memory messages from the network service modules thathave the same message identification number as messages transmitted inthe RCN-packet signal from the first remote cell node to theintermediate data terminal. The message identification number isillustrated in a typical NSM-data packet in FIG. 3.

FIG. 1 illustrates a plurality of the network service modules 110. Thenetwork service modules 110 are set out in a pattern across the groundwhich is dependent upon the positions of the utility usage whichgenerally does not have any particular pattern and the density will varysignificantly for different locations.

The remote cell nodes 112 are arranged in an array with the spacingbetween the remote cell nodes 112 relative to the network servicemodules 110 so that each remote cell node 112 can transmit to at leasttwo and preferably four of the remote cell nodes 112. Thus, the remotecell nodes 112 are provided in significantly larger numbers than isabsolutely necessary for each network service module 110 to be receivedby a respective one of the remote cell nodes 112. The remote cell nodes112 theoretically receive high levels of duplicate information. In anormal residential situation, the location of the remote cell nodes 112so that each network service module 110 can be received by four suchremote cell nodes 112 would lead to an array in which each remote cellnode 112 would be responsive to approximately 1,000 of the networkservice modules 110.

Each of the network service modules 110 is arranged to calculate anaccumulated value of utility usage for a set period of time which in theexample shown is eight hours. Subsequent to the eight hour period, theNSM controller 314 prepares to transmit the information in a packet ofdata as an NSM-packet signal. The packet of data includes:

(a) The total of usage during the set period, i.e. eight hours.

(b) The accumulated total usage stored in the NSM memory 315 to date.The transmission of this information ensures that even if a message islost so that the total for one of the time periods is not communicatedto the central data terminal, the central data terminal 120 canrecalculate the amount in the missing time periods from the updatedaccumulated total.

(c) Some or all of the tamper signals defined above.

(d) The time of transmission.

(e) A message number so that the messages are numbered sequentially. Inthis way, again the remote cell node 112 can determine whether a messagehas been lost or whether the information received is merely a duplicatemessage from a duplicate one of the receiving stations.

(f) “Housekeeping information” concerning the status of the networkservice module 110, for example, the temperature and the battery levelindicator sensor values.

When information is received at the remote cell node 112, the RCNcontroller 414 acts to store the information received in the RCN memory415 and then to analyze the information. The first step in the analysisis to extract from the received messages the identification coderelating to the respective network service module 110. The informationrelating to that network service module 110 is introduced into a RCNmemory register relating to that network service module 110 to updatethe information already stored.

One technique for avoiding transmission of duplicate information fromthe remote cell nodes 112 to the intermediate data terminal 114 can beused in which each remote cell node 112 monitors the transmissions ofthe other remote cell nodes 112. When the signals are monitored, theinformation transmitted is compared with information stored in any otherremote cell node 112 doing the monitoring and if any information isfound in the memory of the remote cell node 112 which is redundant, thatinformation is then canceled. In this way when very high levels ofredundancy are used, the time for transmission from the remote cell node112 to the intermediate data terminal is not significantly increased.

In addition to the transmission periodically of the usage data, eachnetwork service module 110 can be arranged to transmit an alarm signalupon detection of the removal of the electric voltage. The transmissionof the alarm signal can be delayed by a short random period of time sothat if the loss of the voltage is due to a power outage covering anumber of locations all signals are not received at the same time. Theremote cell nodes 112 and intermediate data terminals 114 also can beprogrammed to retransmit such alarm signals immediately. In this way thecentral data terminal 120 has immediate information concerning any poweroutages including the area concerned. This can, of course, enable morerapid repair functions to be initiated.

Furthermore, the remote cell nodes 112 can be arranged to transmitcontrol signals for operating equipment within the premises in which thenetwork service module 110 is located. The remote cell nodes 112 arenecessarily arranged in a suitable array to transmit such information sothat it is received in each of the premises concerned using againrelatively low transmission power and using the equipment provided forthe meter reading system. This transmission capability can be used tocontrol, for example, radio controlled switches within the premises ofrelatively high power equipment for load shedding at peak periods. Insimilar arrangements the network service module 110 may include areceiving facility to enable detection of signals transmitted by theremote cell nodes 112. In one example, these signals may relate tosynchronizing signals so that each of the network service modules 110 isexactly synchronized in time with the remote cell node 112 and/orintermediate data terminal 114 and central data terminal 120. This exactsynchronization can be used for accurately detecting usage duringspecific time periods so that the utility may charge different rates forusage during different time periods for the purpose of particularlyencourage use at non-peak times again for load shedding purposes.

The attenuation of a radio signal is proportional to the inverse of thedistance from the source to the power N. In free space N is equal to 2.In more practical examples where buildings, trees and other geographicalobstructions interfere with the signal N generally lies between 4.0 and5.0. This effect, therefore, significantly reduces the distance overwhich the signal from the network service module can be monitored. Thus,the number of network service modules is significantly reduced which canbe monitored by a single remote cell node.

Furthermore, the large N rapidly reduces the signal strength after apredetermined distance so that while a network service module can beeffectively monitored at a certain distance, the signal strength rapidlyfalls off beyond that distance. This enables the cells defined by eachremote cell node 112 to be relatively specific in size and for thedegree of overlap of the cells to be controlled to practical levelswithout wide statistical variations.

An advantage of the present system is that network service modules 110which are located at a position which is geographically verydisadvantageous for transmission to the closest remote cell node 112 maybe monitored by a different one of the remote cell nodes 112. Thus, inconventional systems some of the network service modules 110 may not bemonitored at all in view of some particular geographical problem. In thepresent invention this possibility is significantly reduced by the factthat the network service module 110 concerned is likely to be in aposition to be monitored by a larger number of the remote cell nodes 112so that the geographical problem most probably will not apply to all ofthe remote cell nodes.

The increased density of remote cell nodes 112 permits the networkservice modules 110 to operate with an integral NSM antenna 322 whichcan be formed as part of the meter reading unit housed within theconventional electric utility meter. In this way the network servicemodule 110 can be totally self contained within the meter housing thusallowing installation within a very short period of time, avoidingcustomer dissatisfaction caused by wiring problems and reducing thepossibility of damage to a separately mounted NSM antenna 322. Inaddition this arrangement significantly reduces the cost of the networkservice module 110 to a level which is economically viable to allowinstallation of the system.

The present invention can employ a system in which the network servicemodules 110 are permitted to transmit only during a predetermined timeperiod so that an open time period is available for communication on thesame frequency between the intermediate data terminal 114 and the remotecell node 112 without any interference from the remote cell nodes 112.This level of communication can be carried out using a polling systemfrom the intermediate data terminals 114 to each of the remote cellnodes 112 in turn preferably including a directional transmission systemat the intermediate data terminal 114. This system allows optimizationof the remote cell node 112 density to meet cost/performance criteria indifferent deployment scenarios.

The present invention, by recognizing the non-volatile nature of theinformation source and the acceptability of missing an occasional updatethrough transmission errors or collisions enables the implementation ofdata collection networks of greater simplicity and at lower cost than ispossible with established communication network approaches involvingtwo-way communication. The present invention, therefore, provides aradio communication network which can be employed to acquire data from alarge number of remote meter monitoring devices disposed over a widearea using very low power transmitters in conjunction with an array ofremote cell nodes all operating on a single radio communication channelor frequency.

Intermediate Data Terminal

The plurality of intermediate data terminals 114 are located within thegeographic area and are spaced to form a grid overlaying the geographicarea. The intermediate data terminals 114 typically are spaced to coverlarge geographic areas. Intermediate data terminals 114 preferably arespaced to provide overlapping coverage, so that on an average, anRCN-packet signal transmitted from a remote cell node 112 is received bytwo or more intermediate data terminals.

As illustratively shown in FIG. 10 each intermediate data terminal 114includes first IDT-transmitter means, second IDT-transmitter means,IDT-memory means, IDT-processor means, first IDT-receiver means, secondIDT-receiver means and an IDT antenna. The first IDT-transmitter means,second IDT-transmitter means, IDT-memory means, IDT-processor means,first IDT receiver means and second IDT-receiver means may be embodiedas a first IDT transmitter 518, second IDT transmitter 519, IDT memory515, IDT processor 514, first IDT receiver 521 and second IDT receiver522, respectively. The first IDT transmitter 518 and the first IDTreceiver 521 are coupled to the IDT antenna 522. The IDT processor 514is coupled to the first and second IDT transmitters 518, 519, the firstand second IDT receivers 521, 522 and IDT memory 515. The second IDTtransmitter 519 and second IDT receiver 522 may be embodied as a devicesuch as a modem 523.

The first IDT transmitter 518 under the control of the IDT processor514, includes a synthesizer or equivalent circuitry for controlling thecarrier frequency, and allowing the first IDT transmitter 518 to changecarrier frequency. The first IDT transmitter 518 transmits preferably atthe first carrier frequency, or the second carrier frequency, the firstpolling signal using a first polling-access protocol to the plurality ofremote cell nodes 112. When the first polling signal is received by aremote cell node, that remote cell node responds by sending theRCN-packet signal to the intermediate data terminal 114 which sent thefirst polling signal. If the intermediate data terminal 114 successfullyreceives the RCN-packet-signal, then the first IDT transmitter 518 sendsan acknowledgment signal to the remote cell node. Upon receiving theacknowledgment signal, the RCN processor 414 at that remote cell nodedeletes, from the RCN memory 415, the data sent in the RCN-packet signalto the intermediate data terminal.

Intermediate data terminals 114 also communicate timing information andcommand signals to remote cell nodes 112. Remote cell nodes 112 servingimportant SCADA functions can be polled more frequently by anintermediate data terminal 114 to reduce network response time.

The first IDT receiver 521 receives the RCN-packet signal transmitted atthe first carrier frequency from the remote cell node which was polled.Thus, after sequentially polling a plurality of remote cell nodes 112,the first IDT receiver 521 has received sequentially in time a pluralityof RCN-packet signals.

The IDT memory 515 stores the received RCN-packet signals. The IDTprocessor 514 collates the NSM-packet signals embedded in the RCN-packetsignals received from the plurality of remote cell notes, identifiesduplicates of NSM-packet signals and deletes the duplicate NSM-packetsignals, i.e., messages from network service modules that have the samemessage identification number.

In response to a second polling signal from a central data terminal 120,the second IDT transmitter 519 transmits a plurality of RCN-packetsignals as an IDT-packet signal to the central data terminal 120. Thesecond IDT transmitter 519 and second IDT receiver 522 may be embodiedas a modem 523 or other device for communicating information over acommunications medium 525 linking the intermediate data terminal withthe central data terminal.

The intermediate data terminals 114 may include one or more directionalantennas 522. During the quiet time, the intermediate data terminal 114is arranged to direct the antenna 522 or antennas to each of the remotecell nodes 112 in turn and to transmit to the respective remote cellnode 112 the first polling signal calling for the remote cell node 112to transmit the stored information from the RCN memory 415. Use of morethan one antenna can allow communication with more than one remote cellnode 112 at a time. The remote cell node 112 is required, therefore,merely to transmit the information upon request in a collated package ofthe information which is transmitted to the intermediate data terminal114 and collected for analysis.

Central Data Terminal

At the upper level of the hierarchy is a central data terminal 120 whichacts as a network control center and data consolidation point. Thecentral data terminal 120 controls basic network operation, allowing itto make global decisions regarding network organization. The centraldata terminal's purpose is to integrate information from a variety ofnetwork nodes into a coherent form which may be forwarded to differentutility operating groups for specific applications. In addition tolinking regional data terminals, the central data terminal 120 isconnected to critical SCADA sites some of which may be co-located withintermediate data terminals 114 at sub-stations. At this level, thereare relatively few communication links, so those required can beselected to optimize cost, speed and reliability. The transmissionbetween the central data terminal 120 and the plurality of intermediatedata terminals 114 is carried out using a communications medium 525 suchas telephone lines, T1 carriers, fiber ontic channels, coaxial cablechannels, microwave channels, or satellite links.

As illustratively shown in FIG. 11, the central data terminal (CDT) 120includes CDT-transmitter means, CDT-receiver means, CDT-processor meansand CDT-memory means. The CDT-transmitter means, CDT-receiver means,CDT-processor means and CDT-memory means may be embodied as a CDTtransmitter 618, CDT receiver 616, CDT processor 614 and CDT memory 615,respectively. The CDT transmitter 618 and CDT receiver 616 are coupledto the communications medium 525. The CDT processor 614 is coupled tothe CDT transmitter 618, CDT receiver 616 and CDT memory 615. The CDTtransmitter 618 and CDT receiver 616 may be a modem 625 or other devicesuitable for communicating information over the communications medium525 between the central data terminal 120 and each intermediate dataterminal 114.

The CDT transmitter 618 transmits sequentially in time the secondpolling signal using a second polling access protocol to the pluralityof intermediate data terminals 114. The CDT receiver 616 receives aplurality of IDT-packet signals. The CDT processor 614 decodes theplurality of IDT-packet signals as a plurality of NSM data. The CDTprocessor 614 also identifies duplicates of NSM data and deletes theduplicate NSM data. The CDT memory 615 stores the NSM data in a database. The NSM data is outputted, analyzed or processed as desired.

Utility Overview

The performance of the network is in large part determined by thenetwork service module 110 to remote cell node 112 link performance,which is defined by the network service module message loss rate. Thenetwork architecture is designed to minimize the network service modulemessage loss rate, which is defined as the fraction of transmittednetwork service module messages which are not received by the remotecell nodes. The two issues that affect the message loss rate are:

1. relatively large and varying pathloss which is caused by the natureof the urban propagation environment; and

2. simultaneous message transmissions, or collisions, which are aproblem for any multiple-access system.

The issue of large and varying pathloss is resolved through the use of:

1. transmit power adjustment;

2. path redundancy, controlled by the remote cell node grid spacing; and

3. multiple transmissions per day.

The collision issue is resolved using:

1. path redundancy, controlled by the remote cell node grid spacing;

2. multiple transmission per day;

3. partitioning of traffic according to priority; and

4. capture effect.

Remote cell node spacing can be selected to control the path redundancy,thus leading to an adjustable level of performance. Notice that pathredundancy and multiple transmission per day are used to resolve bothissues, and thus are principle features of the wide area communicationsnetwork. The effect of collisions is minimal, so the probability ofreceiving a packet any time during the day is maintained atexceptionally high levels.

The link budget contains all of the gains and losses between the networkservice module power amplifier and the remote cell node receiver, and isused to calculate the maximum pathloss which can be allowed on any link.The minimum receivable signal at the remote cell node is estimated as−115 dBm, which is equal to the sum of the noise floor and the carrierto noise level which is required in order to receive the message (10dB).

Every network service module has many remote cell nodes within receivingrange, which increases the reliability of packet reception. When anetwork service module transmits it has the potential to be received bymany remote cell nodules. Some of the remote cell nodules are in shadowfading zones and do not receive the signal whereas others have anincreased signal due to shadowing.

Even though some of the remote cell nodes 112 are quite far from thenetwork service module 110, and thus the average pathloss is below themaximum allowed limit, it is still possible to receive the networkservice module if the signal level fluctuations, shadowing,multipathing, etc., contribute enough to the signal level. Similarly,some remote cell nodes which are close to the network service module donot hear the network service module because the signal variationsdecrease the signal network level by a significant amount.

During the life of the system, the urban landscape changes due tobuilding construction and demolition and foliage growth. These changesin landscape affect the network service module-remote cell node links,causing some remote cell nodes to no longer receive the network servicemodule while new remote cell nodes do receive the network servicemodule. For each link that is no longer available it is expected that anew link becomes operational.

The wide area communications network can readily and cost effectivelyexpand to support new hardware and application software growthscenarios. The wide area communications network can be implemented inthose regions of the user's service territory and for those serviceswhich are most needed on an implementation plan which is not affected bygeographic distribution. FIG. 12 illustrates the configuration of thewide area communications network for serving widely separated geographicareas. This includes the provision of wide area communications networkservices to isolated smaller communities via satellite, fibre optic,microwave or other back bone network. Due to the unique nature of widearea communications network's single channel, micro cellular scatteringpropagation concept, it is immune to traditional radio problems such asfading, nulls, multi-path, lack of line of sight typical of mountainous,hilly, valley or high density urban setting.

The wide area communications network supports a broad range ofmonitoring, verifiable control and fast response transactionapplications. A number of these application needs are and continue to beidentified by utilities. Due to the standardized network interfaceprotocol and message packet configuration, the wide area communicationsnetwork is able to readily augment its service offerings in either newhardware or software. The wide area communications network offers notonly specialized network service modules for electric, gas and watermeters but also provides a series of generic modules with industrystandard in/output interfaces for contact closure, voltage or currentsensing. This allows a variety of vendors to incorporate a wide areacommunications network communication interface into their own productsbe they fuses, alarms, temperature sensors, etc.

The wide area communications network can provide a single integrateddata channel for other utility operational applications. Some of theseapplications are hardware oriented but many are application softwareoriented. They involve the generation of new value-added informationreports or services. Although some are primarily for use by the utility,many of them could be offered for sale to the customer thus resulting ina new revenue stream for the utility.

The wide area communications network can support the expansion of SCADAdue to its highly reliable wireless communication capabilities. Manyutilities would like to add instrumental monitoring points to theirSCADA, however, the wiring costs or difficulties often associated withthese prohibits SCADA growth at a sub-station or other site. Genericnetwork service modules could be used to solve these problems.

The hierarchical design of wide area communications network allows thecustomer to service an arbitrarily large contiguous or non-contiguousgeographic area, as shown in FIG. 12, containing many applications and alarge number of end points.

The key issues related to expansion are:

1. The size and arrangement of the geographic area;

2. The number of end points which can be serviced; and

3. The ease with which the number of applications can be increased.

The hierarchical design of the network allows non-contiguous areas to beserviced over a wide geographic area. Separate areas have their ownintermediate data terminal communicating with the central data terminal.Data from non-contiguous areas would be transferred at the central dataterminal level.

As the number of end points increases, either due to an increase in thenumber of applications in a geographic area or due to an increase in thesize of the geographic area being serviced, the network trafficincreases. The amount of additional traffic created depends on the typeof application being added. Traffic increases in the wide areacommunications network are dealt with by hardware expansion at thecentral data terminal and by installation of additional intermediatedata terminals in the new area. FIG. 13 illustrates a typicalcommunications network with gradual growth in the number of areasserved.

As the number of end points increases, another issue of concern is theidentification of the message source. Wide area communications networkprovides over one trillion serial numbers for each type of servicemodule, which allows unique module identification over the life of thesystem.

As the number of applications increases, the amount of traffic from agiven square mile is assumed to also increase. Simulations to thepresent time have indicated that more than 20,000 end points can beserviced per square mile, with this maximum number depending on thedetails of remote cell node deployment, house density and messagereporting frequency. A dense urban area with 35 ft. by 100 ft. lotscontains approximately 5,000 homes per square mile.

Centralized control of wide area communications network is achieved byallowing the central data terminal to have access to network statusdata, which it uses to make decisions regarding network optimization.These decisions are downloaded to the intermediate data terminals andremote cell nodes as required.

Centralized traffic control is achieved at the remote cell node andintermediate data terminal levels by using priority tables, messagestorage instructions and alarm storage instructions. The structure ofthe priority tables is described as follows.

In each message that is transferred through the system, there is a setof identification tags stating the message type and the source. Thepriority tables in the remote cell nodes 112 and intermediate dataterminals 114 contain a listing of all identification tags in the systemand the priority tables are first installed at the time of deployment,but can be updated from the central data terminal 120 as required.During the network operational period there may be a need to changemessage priorities, which can then be performed with minimal impact onthe network traffic.

Control of the alarm traffic within the network requires another tablebecause alarm reporting generates higher traffic levels for a shortperiod of time. This bursty traffic generation can lead to congestionproblems, and so an alarm instruction table allows the central dataterminal to clear alarm messages out of remote cell node andintermediate data terminal buffers at the end of the alarm. Thispriority table also allows the utility to tailor the alarm traffic delayto suit its particular needs.

Both the priority tables and the alarm instructions are used by themessage storage instruction module to properly manage traffic on thenetwork. The message storage instructions maintain the message queue,ensure that response times are within specification, and transmitperformance data to the central data terminal to be used for networkcontrol.

The network service modules transmit messages to the remote cell nodes,which then use the tables discussed above to organize the message queue.All messages reach the application switch with the specified delay. Thecentral data terminal downloads data to the three control modules andtables as required.

It will be apparent to those skilled in the art that variousmodifications can be made to the communications network for collectingdata from remote data generating stations of the instant inventionwithout departing from the scope or spirit of the invention, and it isintended that the present invention cover modifications and variationsof the communications network provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A data collection system for data collection froma plurality of meters comprising: a) a plurality of telemetry devices,each of the plurality of telemetry devices being associated with atleast one selected meter, each telemetry device including; i) a sensorto measure a parameter at a series of measurement time to generate aseries of successive measurements, ii) a first memory configured tostore a plurality of measurements from said series of successivemeasurements, and iii) a wireless transmitter for transmitting by awireless signal a packet of said plurality of stored measurements, thepacket including an address unique to a certain telemetry device, to acollection device at a series of transmission times, each of said storedmeasurements transmitted at a plurality of different transmission times,each packet being transmitted redundantly in a plurality oftransmissions; and b) a plurality of collection devices, there beingfewer collection devices than telemetry devices, each of the pluralitycollection devices being located remote from the telemetry devices, saidcollection devices including i) a receiver to receive wireless packettransmissions from a subset of said plurality of telemetry devices, ii)a processor for extracting said series of successive measurements from aseries of said transmissions and analyzing said series of successivemeasurements to generate a metered function of said parameter, and iii)a transmitter to transmit data related to the received packettransmissions to a monitoring station.
 2. The data collection system ofclaim 1 wherein a plurality of collection devices are disposed relativeto a certain telemetry device such that the packet of said plurality ofstored measurements transmitted by the certain telemetry device arereceivable by the plurality of collection devices.
 3. The datacollection system of claim 1 wherein said telemetry devices furtherinclude a first timer for timing a predetermined time interval, whereinan expiration of said predetermined time interval causes said sensor tosense a measurement.
 4. The data collection system of claim 1 whereinsaid telemetry device first memory is configured to store a number, saidfirst memory incrementing said number each time a measurement isgenerated, said stored number being transmitted by said transmitter in acurrent transmission from said telemetry device, the data representingsaid telemetry device storing a number transmitted in a previouswireless packet transmission from said telemetry device; and saidcollection devices receiving the wireless packet transmission comparingthe number transmitted in the current wireless packet transmission thenumber transmitted in the previous wireless packet transmission.
 5. Thedata collection system of claim 1 wherein said measured parameterincludes a time-of-use profile.
 6. The data collection system of claim 1wherein said measured parameter is a demand profile.
 7. The datacollection system of claim 1 wherein each of the plurality of saidtelemetry devices includes means for detecting a power failure, thetelemetry device first memory being configured to store power failureinformation, the store power failure information including whether eachstored measurement was generated following a power failure, said powerfailure information being transmitted by said transmitter at at least afirst transmission time.
 8. The data collection system of claim 7wherein said measured parameter includes a load usage profile.
 9. Thedata collection system of claim 1 wherein said collection devicesfurther include a second memory configured to store data representingeach telemetry device of the plurality of telemetry devices from whichthe respective collection device receives a wireless packettransmission.
 10. The data collection system of claim 9 wherein saidcollection devices further include a clock for determining a receipttime of a current wireless packet transmission from a telemetry device,and the data representing said telemetry device including a receipt timeof a previous wireless packet transmission from said telemetry device.11. The data collection system of claim 10 wherein said collectiondevice further includes a processor to compare a message number of thecurrent wireless packet transmission to a message number of the previouswireless packet transmission.
 12. A method of collecting data related toa metered commodity comprising the steps of: a) measuring a parameterrelated to the metered commodity with a sensor at a plurality of times;b) storing said parameter measurements in a telemetry device; c) thetelemetry device transmitting by wireless signal said stored parametermeasurements to at least one collection device at a series oftransmission times; d) extracting said series of successive measurementsfrom a series of said transmissions with said collection device; e)analyzing said series of successive measurements to generate a meteredfunction of said parameter with said collection device; and f)transmitting said parameter measurements to a monitoring station. 13.The method of claim 12 further comprising the step of waiting a selectedperiod of time following a parameter measurement before transmission bythe telemetry device to the collecting device.
 14. The method of claim12 wherein said parameter is selected from the group consisting ofelectrical power, fluid flow, voltage, current, and temperature.
 15. Themethod of claim 12 further comprising the steps of: generating a newnumber in said telemetry device each time a measurement is generated,transmitting said new number with the parameter measurements, andcomparing a previous number to the new number at said collection device.16. The method of claim 15 further comprising the steps of: determiningwhich parameter measurements are new parameter measurements; anddetermining if there are missing parameter measurements.
 17. The methodof claim 15 further comprising the step of storing at least one previousnumber in said telemetry device, and wherein the step of generating saidnew number includes incrementing said at least one previous number. 18.A network for collecting data generated by a plurality of sensors, atleast one sensor being operably coupled to a meter, the meter formetering a commodity, comprising: a) a plurality of data generatingdevices including i) a sensor to measure a meter parameter to generatemeasurements, ii) a memory configured to store said meter parametermeasurements, and iii) a wireless transmitter to transmit by wirelesssignal said store d meter parameter measurements to an intermediatedevice at a plurality of transmission times; and b) a plurality ofintermediate devices, there being fewer intermediate devices than datagenerating devices, said intermediate devices including i) a receiver toreceive transmissions relating to the meter parameter measurements froma subset of said plurality of data generating devices, ii) a processorfor extracting said meter parameter measurements from said transmissionsand analyzing said measurements to generate a metered function of saidparameter, and iii) a wireless transmitter to transmit by wirelesstransmission a signal related to the meter parameter measurements; andc) a central station for receiving said transmitted signal from saidplurality of intermediate devices.
 19. A data collection system for datacollection from a plurality of meters comprising: (a) a plurality oftelemetry devices, each of the plurality of telemetry devices beingassociated with at least one selected meter, each telemetry deviceincluding: (i) a sensor to measure a parameter at a series ofmeasurement time to generate a series of successive measurements, (ii) afirst memory configured to store a plurality of measurements from saidseries of successive measurements, and (iii) a wireless transmitter fortransmitting by a wireless signal a packet of said plurality of storedmeasurements, the packet including an address unique to a certaintelemetry device, to a collection device at a series of transmissiontimes, each of said stored measurements transmitted at a plurality ofdifferent transmission times, each packet being transmitted redundantlyin a plurality of transmissions; and (b) a plurality of collectiondevices, there being fewer collection devices than telemetry devices,each of the plurality collection devices being located remote from thetelemetry devices, said collection devices including (i) a receiver toreceive wireless packet transmissions from a subset of said plurality oftelemetry devices, (ii) a processor for extractings aid series ofsuccessive measurements from a series of said transmissions andanalyzing said series of successive measurements to generate a meteredfunction of said parameter, (iii) a transmitter to transmit data relatedto the received packet transmissions to a monitoring station, (iv) asecond memory configured to store data representing each telemetrydevice of the plurality of telemetry devices from which the respectivecollection device receives a wireless packet transmission, (v) a clockfor determining a receipt time of a current wireless packet transmissionfrom a telemetry device, and (vi) the data representing said telemetrydevice including a receipt time of a previous wireless packettransmission from said telemetry device.
 20. The data collection systemof claim 19 wherein a plurality of collection devices are disposedrelative to a certain telemetry device such that the packet of saidplurality of stored measurements transmitted by the certain telemetrydevice are receivable by the plurality of collection device.
 21. Thedata collection system of claim 19 wherein said telemetry devicesfurther include a first timer for timing a predetermined time interval,wherein an expiration of said predetermined time interval causes saidsensor to sense a measurement.
 22. The data collection system of claim19 wherein said collection device further includes a processor tocompare a message number of the current wireless packet transmission toa message number of the previous wireless packet transmission.
 23. Thedata collection system of claim 19 wherein: said telemetry device firstmemory is configured to store a number, said first memory incrementingsaid number each time a measurement is generated, said stored numberbeing transmitted by said transmitter in a current transmission fromsaid telemetry device, the data representing said telemetry devicestoring a number transmitted in a previous wireless packet transmissionfrom said telemetry device; and said collection devices receiving thewire less packet transmission comparing the number transmitted in thecurrent wireless packet transmission the number transmitted in theprevious wireless packet transmission.
 24. The data collection system ofclaim 19 wherein: said measured parameter includes a time-of-useprofile.
 25. The data collection system of claim 19 wherein saidmeasured parameter is a demand profile.
 26. The data collection systemof claim 19 wherein: each of the plurality of said telemetry devicesincludes means for detecting a power failure, the telemetry device firstmemory being configured to store power failure information, the storepower failure information including whether each stored measurement wasgenerated following a power failure, said power failure informationbeing transmitted by said transmitter at at least a first transmissiontime.
 27. The data collection system of claim 26 wherein said measuredparameter includes a load usage profile.
 28. A method of collecting datarelated to a metered commodity comprising the steps of: (a) measuring aparameter related to the metered commodity with a sensor at a pluralityof times; (b) storing said parameter measurements in a telemetry device;(c) the telemetry device transmitting by wireless signal said storedparameter measurements to at least one collection device at a series oftransmission times; (d) extracting said series of successivemeasurements from a series of said transmissions with said collectiondevice; (e) analyzing said series of successive measurements to generatea metered function of said parameter with said collection device; and(f) transmitting said parameter measurements to a monitoring station;(g) generating a new number in said telemetry device each time ameasurement is generated; (h) transmitting said new number with theparameter measurements; and (i) comparing a previous number to the newnumber at said collection device.
 29. The method of claim 28 furthercomprising the step of waiting a selected period of time following aparameter measurement before transmission by the telemetry device to thecollecting device.
 30. The method of claim 28 wherein said parameter isselected from the group consisting of electrical power, fluid flow,voltage, current, and temperature.
 31. The method of claim 28 furthercomprising the steps of: determining which parameter measurements arenew parameter measurements; and determining if there are missingparameter measurements.
 32. The method of claim 31 further comprisingthe step of storing at least one previous number in said telemetrydevice, and wherein the step of generating said new number includesincrementing said at least one previous number.